Method of casting copper bars having minimum surface oxide



Sept. 1,,1970 HIROSHI NOMURA ET AL 3,526,265

METHOD OF CASTING COPPER BARS HAVING MINIMUM SURFACE OXIDE Filed May 1, 1968 INVENTOR: Hmaifl/ Ara/1 (/24 MINA 4 74/143090 :5 YA

ATTORNEY! United States Patent Oflice 3,526,265 METHOD OF CASTING COPPER BARS HAVING MINIMUM SURFACE OXIDE Hiroshi Nomura, Michio Minakawa, and Takeshi Seya, Hitachi-shi, Japan, assignors to Hitachi Cable Ltd., Tokyo, Japan Filed May 1, 1968, Ser. No. 725,715

Claims priority, application Japan, May 15, 1967,

42/30,372 Int. Cl. B22d 21/04 US. Cl. 164--66 8 Claims ABSTRACT OF THE DISCLOSURE The present disclosure is directed to a method of casting a copper bar in a horizontal vessel-type casting mold, said method comprising pouring molten copper into said mold to a predetermined level relatively near the open top of said mold, closing the open top of said mold with a removable lid after completion of said pouring but before a copper-copper oxide eutectic is formed in the surface layer of said molten copper, disposing the inner surface of said lid spaced from the level of molten copper in said mold at such a distance that splashing molten copper will not be excessively attached to said surface and convection of air above said surface is substantially completely prevented, allowing the molten copper to cool and solidify, removing said lid and removing the solidified copper bar from said mold.

The present invention relates to a method of casting a copper bar which is used in the electric cable industry or the copper rolling industry, and more particularly to an improved method of casting the copper bar.

Copper bars are generally cast in a horizontal vesseltype casting mold. According to this method, however, the surface layer of the molten copper tends to absorb oxygen in the atmosphere because it is exposed to the atmosphere during the casting operation and the solidification of the copper, and as a result a substantial thickness of oxide layer (eutectic of Cu and Cu O) is formed on that portion of the surface of the resultant copper bar in particular which was exposed to the atmosphere during the casting operation. Such an oxide layer remains in the final copper bar since it is not removed in the subsequent processes. Since the eutectic is relatively brittle per se, it produces the problem that the mechanical properties of the eutectic-containing copper bar are degraded as a whole. In order to minimize the formation of such oxide layer, a continuous casting method has been proposed. However, this method has the disadvantages that the cost is high as compared with the first-mentioned method using a horizontal casting mold and therefore is not adaptable to the casting of a small quantity of copper bars. Also, the productivity is low relative to the high facility cost. Because of the reasons set forth above, the former method which is inexpensive and adaptable to mass production is still being employed in the art dominantly forthe production of copper bars.

It is, therefore, an object of the present invention to provide a novel method of casting a copper bar using a horizontal casting mold, by which the copper bar can be produced at low costs with a minimum oxide layer being produced on the surface thereof.

It is another object of the present invention to provide a novel method of casting copper bar, which minimizes the oxide layer formed on the product copper bar and enables a horizontal casting mold to be used which is simple in structure, easy in handling and therefore high in workability.

3,526,265 Patented Sept. 1, 1970 According to the present invention, there is provided a method of casting a copper bar by the use of a horizontal vessel-type mold, which comprises pouring molten copper in the casting mold at a temperature of 1l50 to 1200 C., closing the open top end of the casting mold with a removable lid within about seconds after pouring in such a manner that the undersurface of said lid is spaced about 70 mm. or less from the level of the molten copper to thereby prevent convection of the air above the surface of said molten copper, allowing the molten to cool to solid in that state and removing the lid to take out the solidified bar copper from the casting mold.

The term casting mold as used herein refers to any of conventional vessel-type casting molds which are commonly used in the casting of copper bar, including the casting molds with three to five pouring gates as used in the Walker-type and Clark-type casting machines. The lid consists of a heat-resistant steel plate or an asbestos plate and is removably placed on the open top end of the casting mold. The word removably here is to be understood to mean that the lid is of such structure that it can be placed on the casting mold as quickly as required or can be placed on the casting mold automatically when said casting mold has reached a predetermined position during rotation of said casting mold at a predetermined frequency. The position and the time at which the lid is placed on the casting mold are also critical in practicing the inventive method. In casting copper bars of 113 to kilograms in weight, which are common in the art, it is preferable that the inner surface of the lid is spaced about 70 mm. or less from the level of the molten copper in the casting mold, through slightly variable depending upon the size of the desired copper bar. This is because convection of air in the space defined by the inner surface of the lid and the level of the molten copper can be prevented completely when the height of said space is within 70 mm. but cannot be stopped when said height exceeds 70 mm.

As regards the time at which the lid is placed 'on the casting mold, a satisfactory result can be obtained when the open end of the casting mold is covered with the lid within about 30 seconds after pouring the molten copper and in this case the formation of the Cu-Cu O eutectic, which constitutes the surface oxide layer, can be minimized. In order to facilitate closure of the casting mold, the top opening of the casting mold may be previously covered with a separate closure member to the extent of about 60 to 70% thereof, so that the remaining opening only need may be covered with the lid after pouring the molten copper.

The results of the various experiments conducted by the present inventors have revealed that formation of the Cu-Cu O eutectic due to convection of air can be suppressed more effectively when the air space between the lid and the molten copper surface is reduced, provided that said lid is not in direct contact with said molten copper. In order to eliminate the convection of air completely, the air in the air space between the lid and the surface of molten copper may be substituted with an inert gas or a reducing gas by blowing the latter into said air space after the top opening of the casting mold has been closed with the lid, thereby preventing the formation of the surface oxide layer. The gases which can be used for this purpose in practicing the inventive method industrially, include argon gas, nitrogen gas and other various converted gases such, for example, as steam. In practice, these gases are introduced into the casting mold through a gas inlet pipe connected with the lid upon completion of pouring of the molten copper. Thereafter, the molten copper is allowed to solidify without contacting it with air, whereby forrnation'of the oxide layer on the surface of the copper bar can be completely prevented. The lid is only required to roughly seal the air space interior of the casting mold against the atmosphere and thus there is no need for producing a superatmospheric pressure in said air space. As stated previously, the lid should not be placed in contact with the surface of molten copper. This is necessary for the purpose of enabling hydrogen gas to be released from the molten copper as the molten copper is cooled.

Other features and advantages of the present invention will become apparent from the following detailed description of embodiments of the invention when taken in conjunction with the accompanying drawings, in which:

FIGS. 1 to 3 inclusive are cross sectional views illustrating different forms of the casting mold unit to be used for practicing the method of this invention;

FIG. 4 is a'lOOX microscopic picture diagrammatically showing the structure of the surface layer of a copper bar cast according to the method of this invention; and

FIG. 5 is a microscopic picture, similar to FIG. 4, di agrammatically showing the structure of the surface layer of a copper bar cast according to the conventional method.

Referring to FIGS. 1 to 3, reference numeral 1 designates a horizontal vessel-type casting mold defining a casting pit 2 therein. Immediately after pouring molten copper 8 into the casting pit 2, a steel lid 5 is placed on the top surface 4 of the casting mold 1 to prevent convection of air in an air space 9 above the surface of the molten copper. In this case, the inner surface of the steel lid 5 should be spaced several tens of millimeters from the level of molten copper 8.

According to the arrangement shown in FIG. 1, the steel lid 5 is merely placed on the top surface 4 of the casting mold 1 and, in order to facilitate the handling, the steel lid 5 is provided with a hook 6 on the upper surface thereof. In the arrangement shown in FIG. 2, the steel lid 5 is provided with at pipe 7 connected thereto, through which an inert gas or a reducing gas is introduced into the air space 9 to replace air in said air space after the steel lid is placed on the casting mold 1. Thus, the formation of oxide layer on the surface of the molten copper 8 can be prevented. Now, in the case of arrangement shown in FIG. 3, a recessed shoulder 3 is formed in the top surface 4 of the casting mold 1 for interlocking engagement with the steel lid 5 which is provided with a hook 6. This arrangement is advantageous in that the air space 9 can be sealed against the atmosphere more positively than the preceding arrangements. Another advantage is that the recessed shoulder 3 serves as a guide for the lid 5, rendering the mounting and removal of said lid easy.

Thus, it will be understood that, according to the present invention wherein the open end of the casting mold .1 is closed with the lid 5 and the molten copper is allowed to cool without being exposed to suffering convection of air or in an inert gas atmosphere, the formation of Cu-Cu O eutectic in the surface layer of the molten copper can be minimized as compared with the conventional methods in which the surface of the molten copper is widely exposed to free convection of air during cooling. Upon cooling, the lid is removed and the solidified copper bar is removed from the casting mold, whereby the desired copper bar of satisfactory quality can be obtained.

The structure of the surface layer 11 of the copper bar 10, cast according to the embodiment of FIG. 3, is diagrammatically shown in the michoscopic picture of FIG. 4, the magnification being 100x. The picture shows that only a very small oxide layer is formed on the surface of the copper bar, and the Cu-Cu O can be observed only between the primary crystals of copper 13 as indicated by numeral 12. By contrast, the bar copper cast by the conventional method, as shown in FIG. 5, has a large amount of Cu-Cu O eutectic 22 (oxide layer) formed in the surface layer 21 thereof, with only a small amount of the primary crystals 23 of copper scattering therein.

4 As a result of the actual measurement on a 113 kilogram copper bar, it has been found that the depth of the Cu-C-u O eutectic layer 22 was as great as 5 to 8 millimeters.

Hard copper wires of 2.6 millimeters in diameter were produced from the copper bar 10 according to the method of the present invention and from the copper bar 20 produced according to the conventional method respectively by cold drawing, and the mechanical properties thereof were compared with each other. Although no substantial difference was observed therebetween with respect to the tensile strength and elongation, it was revealed that the amount of torsion per millimeters of the hard copper ,wire from the copper bar 10 according to the present invention was far greater than that of the hard copper wire from the conventional copper bar 20. Namely, the average number of torsion of 5 samples of the former was 53, whereas that of the latter was only 29.2.

The casting method of the present invention brings about another advantage in that the casting mold to be used for practicing the method can be simple in structure, handled with ease and operated at high workability. In addition, the method of this invention enables a bar copper to be produced with a minimum oxide layer on the surface thereof at low costs. Of course, the copper bar produced according to the present invention does not require a subsequent machining operation as has been required for the conventional one for the removal of the oxide layer, because the surface of the copper bar produced by the invention method is smooth since it bears an extremely small amount of oxide layer and accordingly is free from the wrinkles peculiar to the oxide layer.

What is claimed is:

1. A method of casting a copper bar in a horizontal vessel-type casting mold, said method comprising pouring molten copper into said mold to a predetermined level relatively near the open top of said mold, closing the open top of said mold with a removable lid after completion of said pouring but before a copper-copper oxide eutectic is formed in the surface layer of said molten copper, disposing the inner surface of said lid spaced from the level of molten copper in said mold at such a distance that splashing molten copper will not be excessively attached to said surface and convection of air above said surface is substantially completely prevented, allowing the molten copper to cool and solidify, removing said lid and removing the solidified copper bar from said mold.

2. The method of claim 1 wherein said inner surface of said lid is spaced about 70 mm. or less from the level of the molten copper.

3. The method of claim 1, wherein the open top of said mold is closed with said lid about 30 seconds after pouring is completed. 7

4. The method of claim 1 wherein about 60 to 70% of the open top of said mold is closed prior to pouring.

5. The method of claim 1 wherein an inert or reducing gas is introduced into the space defined by the inner surface of said lid and the level of the molten copper.

6. The method of claim 1 wherein the molten copper is poured into the casting mold at a temperature of about llS0 to 1200 kg. in weight.

7. The method of claim 2, wherein the copper bars to be cast are about 113 to kg. in weight.

8. The method of claim 5, wherein the gas is selected from the group consisting of argon, nitrogen and steam.

References Cited UNITED STATES PATENTS 1,319,500 lO/l9l9 Whalen 164-61 3,268,963 8/1966 Mann 16466 X ROBERT D. BALDWIN, Primary Examiner US. Cl. X.=R. 

